For each round use the dS map picker: http://www.worms-univers.com/worms-armageddon/dsp/you may repick one map or whole set once if all agree (or several times, if things like 2x sonic, 2x smdw, or 2x shiny world happen often).
Enter your nick, and type "WO16" as short description.

MAKE SURE TO CHECK MAPS PAGES (JUST CLICK MAPS NAME IN PICKER RESULT) FOR SPECIAL RULES!!!